Various devices are known that allow adjustment of the longitudinal position of a front stop of a ski-boot binding device with a view to adapting the binding to various boot lengths. A common prior-art solution is based on guide rails positioned on the ski, that include a toothed part on which a complementary toothed part integral with the front stop of the ski binding is positioned. When these toothed parts are released, the stop can be adjusted by being slid longitudinally along the guide rails. However, existing solutions all have drawbacks, including:                they require a tool for releasing the toothed parts. This tool has to be inserted via an opening and held in position during adjustment. In this case, solutions are not user-friendly and are impractical for rapid adjustment operations under any conditions such as, for example, on a ski trail, where the required specific tool is not always available; and/or        there is play present at the join between the two toothed parts, even in the configuration envisaged for skiing, which greatly diminishes control over guiding the ski; and/or        they are not fail-safe, i.e. they can give rise to accidental changes in setting during their use, which is dangerous because it may cause the skier to fall; and/or        they are complicated because they are based either on a large number of elements or on elements that are complicated to manufacture or to assemble; and/or        lastly, they are sometimes unattractive in appearance because unattractive mechanical elements can be seen.        